The board, long-term objective of the proposed research is to determine how ras oncogenes work. Modern molecular genetic and somatic genetic approaches will be used to define the cellular components that interact with ras-encoded proteins and to study the internal workings of ras proteins. Specifically, mutations affecting the effector domain of the p21Hras, the transforming protein of Harvey murine sarcoma virus, will be constructed. The biological activity of these mutations in a tumorigenicity assay will be compared to the results obtained with cultured cells. Additionally, somatic mutations that define cellular elements that interact with ras proteins will be recovered and analyzed. Finally, protein interactions within and between ras proteins will be studied. ras proteins play a role in the development of a substantial fraction of human cancers. Evidence supporting this contention is of two types: 1) ras oncogenes are frequently found to be mutated in human tumors, and, 2) introduction of ras oncogenes into cultured cells, including humans cells, results in the acquisition of lethal tumorigenic phenotypes, as assayed in animals. Ultimately, the results of the proposed research may prove useful in the prevention, diagnosis and treatment of human cancer.